This invention relates generally to gas generators for inflating vehicular inflatable restraint cushions, commonly known as air or gas bags, to provide impact protection to occupants of the vehicle. More particularly, the invention relates to the auto ignition of such gas generators.
It is well known to protect a vehicle occupant using a cushion or bag that is inflated/expanded with gas, e.g., an "air bag", when the vehicle encounters sudden deceleration, such as in a collision. In such systems, the cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the inflatable restraint system, the air bag is commonly inflated in a matter of a few milliseconds with gas produced by the burning of a gas generant material, e.g., a pyrotechnic, in a device commonly referred to as "a gas generator" or "an inflator." The gas generant is commonly ignited by means of an igniter having an ignition agent. The pressure of the combustion gases resulting from the rapid burning of the gas generant material causes gas to rush into the air bag to effect the rapid inflation thereof. The cushion can then serve to restrain the movement of the vehicle occupant as the collision proceeds.
Inflatable restraint systems have been devised for automotive vehicles in which one or more air bags are stored in one or more storage compartments within the vehicle. In general, an air bag provided for the protection of a vehicle driver, e.g., a driver side air bag, is stored within a housing mounted in a storage compartment located in the steering column of the vehicle. Whereas, an air bag for the protection of a front seat passenger, e.g., a passenger side air bag, is typically stored within a housing mounted in the instrument panel/dash board of the vehicle.
In such systems, the gas generators or inflators must be constructed to withstand large thermal and mechanical stresses during the gas generation process. Thus, gas generators have been fabricated using steel for the casing and other structural components, with the structural components commonly joined together by screw threads, roll crimping or welding.
To satisfy light weight specifications, significant weight reduction can be achieved through the utilization of a light metal or material such as aluminum or an aluminum alloy for the generator housing and other structural components. Gas generators made of such materials typically will not experience problems in ordinary use wherein, during the event of a collision, the ignition agent is ignited, followed by the igniting of the gas generant to generate inflation gas. However, the mechanical strength of such lighter weight materials is lowered when overheated to a high temperature.
For example, a problem is encountered when generators utilizing aluminum for the housing construction are subjected to a high temperature environment, such as a bonfire. This problem stems from the fact that at a temperature in the 650.degree. F. (343.degree. C.) range, the pyrotechnics of the gas generator commonly automatically ignite. In this temperature range, the aluminum of the housing structure degrades and tends to rupture or burst, projecting pieces and/or fragments in all directions. This problem is not encountered with gas generators that employ steel in the housing structure since steel does not degrade until a much higher temperature of about 1100.degree. F. (593.degree. C.) is reached. Thus, the use of aluminum, in place of steel, in a gas generator, while serving to reduce the weight of the assembly typically results in the gas generator having a lower internal pressure capability. This lower internal pressure capability could be hazardous in a high temperature environment such as the gas generator might be subjected to in the event of a fire whether in storage, in transit, or after installation in a vehicle.
A previously disclosed solution to the this problem is the incorporation of an auto ignition device in the gas generator. For example, U.S. Pat. No. 4,561,675, Adams et al., assigned to the assignee of the present invention and which patent is incorporated herein in its entirety, discloses an auto ignition device that causes the pyrotechnics in a gas generator to function when the device is subjected to a predetermined high temperature below the ignition temperature of the solid fuel gas generant. The container of the auto ignition device is disclosed as being hat shaped and includes a brim and a crown, with the crown attached in thermal contact with the generator housing and with the area of a wall of the container bound by the brim being closed by a foil seal.
The inclusion of an auto ignition material in an inflator housing such as is used for inflators for driver side installations is also disclosed in U.S. Pat. Nos. 5,106,119 and 5,114,179 which disclose a housing apparatus wherein, by means of a piece of aluminum foil, a "packet" auto ignition material is held in place in a recess formed in the canister cover. Also, U.S. Pat. No. 5,186,491 discloses the incorporation of an auto ignition material within a recess of the gas generator.
In addition, U.S. Pat. Nos. 4,998,751 and 5,109,772, both assigned to the assignee of the present invention and which patents are incorporated herein in their entirety, generally relate to inflator devices and, at least in some specifically described and illustrated embodiments such gas generators having elongated bodies, as are commonly used on the passenger side of an automotive vehicle. These patents disclose the incorporation, respectively, of "an auto ignition device" and "a container" which "holds or contains auto ignition granules" in such gas generators within a centrally located recess. Thus, it is known to place auto ignition granules within a container within such an elongated gas generator housing at one end thereof opposite an end of a elongated igniter tube. Furthermore, it is known to use a cup-shaped container to hold such granules. Such a cup-shaped container has in the past included three equally spaced ribs on the outside thereof allowing for the press fit insertion of the container within the gas generator. In the past, such a cup-shaped container has also included a bendable flange to secure a screen over the mouth of the cup wherethrough the gas resulting from the ignition of the auto ignition material is passed to contact the primary ignition tube granules stored in the gas generator.
As vehicular inflatable restraint systems have and are becoming more prevalent, there is greater interest in automating the assembly process to the extent reasonably and safely possible. The automation of production, however, imposes practical limitations on the shapes and forms of items being handled and produced. This is especially important in the manufacture and assembly of safety systems such as vehicular inflatable restraint systems where the margin for error can be critically small.
Thus, there is a continuing need for improving the suitability of inflatable restraint system designs for automated manufacture and assembly without compromising the operational aspects of such systems whereby protection is provided to an occupant.